KR100637304B1 - Organic el display and active matrix substrate - Google Patents

Abstract

A drive control element 30 including a first terminal and a control terminal and a second terminal connected to the power supply terminal 31, an organic EL element 20 connected between the second terminal and the power supply terminal 34, A first operation of switching the capacitor 38 connected to the control terminal, the video signal input terminal 35 and the second terminal into the connected state in the signal writing period, and switching from the light emitting period to the unconnected state according to the scanning signal. A second for switching the switch 37, the control terminal, and the second terminal into the connected state in the signal write-in period, and switching the non-connected state before the first switch 37 goes into the disconnected state according to the scanning signal; An active matrix organic EL display 1 including a switch 32 is provided.

Organic EL display, active matrix substrate, display element, flat panel display, pixel circuit

Description

ORGANIC EL DISPLAY AND ACTIVE MATRIX SUBSTRATE}

TECHNICAL FIELD The present invention relates to an active matrix display and an active matrix substrate, and more particularly to an active matrix organic EL display including an organic electroluminescent (EL) element as a display element and an active matrix substrate usable therein.

Flat panel displays typified by liquid crystal displays have features such as thinner, lighter weight, and lower power consumption than CRT displays. Due to these features, the demand for flat panel display is growing rapidly.

In an active matrix flat panel display, a switch for electrically separating the on-state pixels and the off-state pixels is provided in each pixel. Usually, the pixel is further provided with a capacitor for holding a video signal. Therefore, this display can realize the favorable display quality without crosstalk between adjacent pixels. For this reason, an active matrix flat panel display is used as a display of various electronic devices including a portable information terminal.

In recent years, development of organic electroluminescent display is actively performed. An organic EL display is a self-luminous display, which is advantageous in realizing a high speed response and a wide viewing angle compared with a liquid crystal display.

Knapp et al., In US Pat. No. 6,373,454 B1, disclose a pixel circuit that can be used in an organic EL display.

1 is an equivalent circuit diagram of a pixel circuit disclosed by Knapp et al. The operation of this circuit is performed in two stages. In the first and second steps, the power supply line 31 is set to the potential V1, and the power supply line 34 is set to the potential V2 higher than the potential V1.

In the first step, first, the switch 33 is opened (0FF), and the switches 32 and 37 are closed (0N). In this state, the signal current is supplied from the video signal wiring 35 to the organic EL element 20 as an input signal. Since the transistor 30 is diode-connected by the switch 32, the capacitor 38 accumulates a voltage equal to the gate-source voltage of the transistor 30 through which the signal current flows. Thereafter, the switches 32 and 37 are opened.

In the second step, the switch 33 is closed to connect the organic EL element 20 and the drain of the transistor 30. Since the voltage corresponding to the input signal is accumulated in the capacitor 38, the organic EL element 20 is supplied with a current almost equal to the input signal.

In this pixel circuit, the switching of the switches 32 and 37, that is, the ON / OFF operation is performed at the same time. Therefore, switching of the switches 32 and 37 can be controlled using the same control line.

However, although these controls are performed using the same control line, switching of the switches 32 and 37 may not be performed at the same time due to variations in the characteristics resulting from the design and the process of the pixel circuit pattern.

When the OFF operation of the switch 32 is performed later than that of the switch 37, in the period from the OFF operation of the switch 37 to the OFF operation of the switch 32, the switch 32 from the gate of the transistor 30 is switched. And the current flows to the power supply line 31 through the transistor 30. As a result, the gate-source voltage of the transistor 30 decreases. Therefore, in this case, gradation distortion may occur. In particular, if the time difference of the OFF operation is nonuniform between pixels, there is a possibility that an in-plane nonuniformity of luminance may occur.

This problem can be avoided by providing a control line for the switch 32 and a control line for the switch 37, respectively, and supplying the OFF signal to the former before supplying the OFF signal to the latter. In this case, however, one control line is increased for each column of the pixels. Therefore, restrictions on pixel layout become strict, and the area in which the individual organic EL elements can be arranged is reduced. When bright display is performed on a small organic EL element, the luminance life is shortened.

<Start of invention>

An object of the present invention is to provide an active matrix organic EL display which can realize excellent display quality with a relatively small number of wirings, and an active matrix substrate usable therein.

According to the first aspect of the present invention, a first terminal connected to a first power supply terminal, a control terminal to which a video signal is supplied from a video signal input terminal, and a magnitude corresponding to a voltage between the control terminal and the first terminal A drive control element having a second terminal for outputting a drive current of; an organic EL element connected between the second terminal and the second power supply terminal; and one electrode connected to the control terminal; And a capacitor capable of maintaining a voltage between the first terminal and the first terminal in a magnitude corresponding to the video signal, and connecting the video signal input terminal and the second terminal in a signal writing period in accordance with a scan signal. A first switch for switching the video signal input terminal and the second terminal into a non-connected state in a light emitting period subsequent to the signal writing period, and in accordance with the scanning signal, In the signal writing period, the control terminal and the second terminal are brought into a connected state, and the switching of the control terminal and the second terminal into a non-connected state is performed before the first switch is turned off. An active matrix organic EL display having a second switch is provided.

According to a second aspect of the present invention, there is provided a first terminal connected to a first power supply terminal, a control terminal, and a second terminal for outputting a driving current having a magnitude corresponding to a voltage between the control terminal and the first terminal. A drive control element provided, an organic EL element connected between the second terminal and the second power supply terminal, a capacitor connected between the electrostatic potential terminal and the control terminal, the video signal input terminal and the second A first switch connected between the terminals, and a second switch connected between the control terminal and the second terminal, wherein a control terminal for controlling switching of the first switch is configured to perform switching of the second switch. It is connected to the control terminal to control, and the active-matrix type organic electroluminescent display with a threshold value of the said 1st switch is shallower than the threshold value of the said 2nd switch is provided.

According to a third aspect of the present invention, there is provided a first terminal connected to a first power supply terminal, a control terminal, and a second terminal for outputting a driving current having a magnitude corresponding to a voltage between the control terminal and the first terminal. A drive control element provided, an organic EL element connected between the second terminal and the second power supply terminal, a capacitor connected between the positive potential terminal and the control terminal, and an input terminal connected to the control signal input terminal. And a delay element having an output terminal for outputting a control signal supplied from a control signal input terminal, a first switch connected between the video signal input terminal and the second terminal, the control terminal and the second terminal. A control terminal for controlling switching of the first switch is connected to the output terminal, and a control terminal for controlling switching of the second switch is connected to the first switch. An active matrix type organic EL display connected to the signal input terminal is provided.

According to a fourth aspect of the present invention, there is provided an active matrix substrate on which an organic EL element is to be formed, comprising: a first terminal connected to a power supply terminal, a control terminal to which a video signal is supplied from a video signal input terminal, and an organic EL element. A drive control element having a second terminal connected thereto and outputting a drive current having a magnitude corresponding to a voltage between the control terminal and the first terminal, and one electrode connected to the control terminal; The capacitor capable of maintaining a voltage between the first terminal to a magnitude corresponding to the video signal, and the video signal input terminal and the second terminal connected in a signal writing period in accordance with a scan signal; A first switch for switching between the video signal input terminal and the second terminal in a non-connected state in a light emitting period subsequent to a signal writing period; The control terminal and the second terminal are connected to the control terminal and the second terminal in the signal writing period in response to the scanning signal and before the first switch is turned off. There is provided an active matrix substrate having a second switch that switches over to a non-connected state.

According to a fifth aspect of the present invention, a pixel electrode, a first terminal connected to a power supply terminal, a control terminal to which a video signal is supplied from a video signal input terminal, and the control terminal and the A drive control element having a second terminal for outputting a drive current having a magnitude corresponding to a voltage between one terminal; and one electrode connected to the control terminal; and a voltage between the control terminal and the first terminal. The capacitor capable of maintaining the size corresponding to the video signal, the video signal input terminal and the second terminal connected to each other in the signal writing period in accordance with the scanning signal, and in the light emitting period following the signal writing period. A first switch for switching the video signal input terminal and the second terminal into a non-connected state, and the signal writing period in accordance with the scanning signal And a second switch for making the control terminal and the second terminal connected, and for switching the control terminal and the second terminal to a non-connected state before the first switch is disconnected. One active matrix substrate is provided.

1 is an equivalent circuit diagram of a conventional pixel circuit.

2 is a plan view schematically showing an organic EL display according to a first aspect of the present invention.

FIG. 3 is a plan view schematically showing an example of a structure that can be employed in a pixel of the organic EL display shown in FIG. 2. FIG.

4 is a timing chart showing an example of a method of driving the organic EL display of FIG. 1;

FIG. 5 is a plan view schematically illustrating a modification of the pixel structure of FIG. 3. FIG.

6 is a cross-sectional view schematically showing an example of a structure that can be employed in a second switch.

FIG. 7 is a sectional views schematically showing an example of a structure that can be employed in a first switch. FIG.

8 is a plan view schematically illustrating an organic EL display according to a second aspect of the present invention.

9 is a diagram illustrating an example of a signal input to a delay element and a signal waveform output by the delay element.

FIG. 10 is an equivalent circuit diagram showing an example of a pixel circuit employable in the organic EL display of FIG. 8. FIG.

FIG. 11 is an equivalent circuit diagram showing another example of the pixel circuit employable for the organic EL display of FIG. 8. FIG.

FIG. 12 is an equivalent circuit diagram showing still another example of the pixel circuit employable for the organic EL display of FIG. 8. FIG.

<Best mode for carrying out the invention>

Some aspects of the present invention will be described with reference to the drawings. In each of the following forms, this invention is applied to an organic electroluminescent display as an example.

2 is a plan view schematically showing an organic EL display according to a first aspect of the present invention. FIG. 3 is a plan view schematically showing an example of a structure that can be employed in pixels of the organic EL display shown in FIG. 2.

The organic EL display 1 includes an insulating substrate 10 such as glass, for example. On the board | substrate 10, the some pixel arranged in matrix form and the drive circuit which drives these pixels are arrange | positioned.

The driving circuit includes a video signal line driver 11, a scan signal line driver 12, a video signal line 35 connected to the video signal line driver 11, and a control line which is a scan signal line connected to the scan signal line driver 12 ( 36, the first power supply line 31, and the second power supply line 34 are included. This drive circuit drives each pixel circuit based on control signals YST, YCLK, XST, and XCLK supplied from the outside, power supply potentials Vdd and Vss, and data signals Iin.

Each pixel includes a display element 20 and a pixel circuit for driving the display element 20. The pixel circuit and the display element 20 are connected in series between a first power supply terminal set at the potential Vdd and a second power supply terminal set at the potential Vss. The first and second power supply terminals are connected to the first power supply line 31 and the second power supply line 34, respectively. In this case, the potential Vdd is set to be higher than the potential Vss.

The display element 20 includes a pair of opposing electrodes and an active layer interposed therebetween. In addition, the "active layer" here is a layer in which optical characteristics, such as a brightness | luminance and a transmittance | permeability, change with the voltage applied between electrodes. In this example, the display element 20 is an organic EL element and has an organic material layer including an organic light emitting layer as an active layer.

The pixel circuit includes the drive control element 30, the capacitor 38, the first switch 37, the second switch 32, and the third switch 33. As the drive control element 30 and the switches 37, 32, and 33, for example, a field effect transistor of the first conductivity type can be used. In this example, p-channel thin film transistors are used as the drive control element 30 and the switches 37, 32, and 33.

The first terminal of the drive control element 30, that is, the source, is connected to the first power supply terminal set to the potential Vdd. One electrode of the capacitor 38 is connected to the control terminal of the drive control element 30, that is, the gate, so as to maintain the potential difference between the first terminal and the control terminal of the drive control element 30 corresponding to the video signal. Here, the capacitor 38 is connected between the first power supply terminal and the control terminal of the drive control element 30. The first switch 37 is connected between the video signal input terminal and the second terminal of the drive control element 30, that is, the drain. The video signal input terminal is connected to the video signal line 35. The second switch 32 is connected between the gate and the drain of the drive control element 30. The control terminals, that is, the gates of the first switch 37 and the second switch 32 are connected to the control line 36 which is a scan signal line. The third switch 33 is connected between the drain of the drive control element 30 and the first electrode 21 of the display element 20.

In this example, the first electrode 21 is an anode, and the second electrode of the display element 20 is a cathode connected to the second power supply terminal set to the potential Vss. In this example, the first power supply terminal is used as the potential terminal to which the capacitor 38 should be connected, but the capacitor 38 is connected between the other potential terminal and the control terminal of the drive control element 30. You may also do it.

In this organic EL display 1, the input terminal of the switch 37 included in each pixel column, that is, the source, is connected to one video signal line 35 common to each column. The video signal line 35 is supplied with a signal current from the video signal line driver 11 as an input signal or a video signal Iin.

In addition, the control terminals of the switches 37 and 32 included in each pixel row, that is, the gate, are connected to one scan signal line 36 in common for each row. The scan signal line 36 is sequentially supplied with a voltage signal as the scan signal Scan from the scan signal line driver 12.

In addition, the removal of at least one electrode and the active layer of the display element 20 from the organic EL display 1 corresponds to the active matrix substrate. This active matrix substrate includes an insulating substrate 10, wirings such as an image signal line 35, a scanning signal line 36 and a power supply line, and a pixel circuit. In addition, the active matrix substrate may optionally include a video signal line driver 11, a scan signal line driver 12, and a first electrode 21 of the display element 20.

In this organic EL display 1, the 1st switch 37 and the 2nd switch 32 can have the same laminated structure, and can be formed simultaneously. For example, these first switches 37 and second switches 32 are thin film transistors having a top gate structure using polysilicon in the semiconductor layer and formed simultaneously.

In this embodiment, the first switch 37 and the second switch 32 are other than setting the channel length L1 of the first switch 37 to be shorter than the channel length L2 of the second switch 32. And, they are designed to have the same structure. Thus, a first switch 37 having a shallower threshold Vth1 and a second switch 32 having a deeper threshold Vth2 are obtained.

For example, as the first switch 37 and the second switch 32, a thin film transistor having a top gate structure (coplanar type) using polysilicon for the semiconductor layer is used. These first switches 37 and second switches 32 adopt the same stacked structure, and they are formed at the same time. For example, the channel widths of the first switch 37 and the second switch 32 are all 3 µm, and the channel lengths of the first switch 37 and the second switch 32 are, for example. 3 micrometers and 4.5 micrometers, respectively. In this way, a first switch 37 having a shallower threshold Vth1 and a second switch 32 having a deeper threshold Vth2 can be obtained.

In each pixel circuit, the gates of the first switch 37 and the second switch 32 are connected to the same scan signal line 36. Therefore, the same control signal is simultaneously supplied to the gates of the first switch 37 and the second switch 32.

When the same OFF signal is supplied to the gates of the first switch 37 and the second switch 32 at the same time, the second switch 32 having a deeper threshold Vth2 is formed of a first having a shallower threshold Vth1. Prior to the OFF operation of the switch 37, the OFF operation is started. That is, in this organic EL display 1, before the 1st switch 37 turns into a non-connection state, the 2nd switch 32 can be made into a non-connection state.

Therefore, it is possible to prevent the OFF operation of the second switch 32 preceding the OFF operation of the first switch 37 and the fluctuation of the gate-source voltage of the drive control element 30 due to it. . Therefore, it is possible to suppress the occurrence of gradation distortion and in-plane unevenness of luminance, and to achieve excellent display quality with a relatively small number of wirings.

The channel length of the 1st switch 32 and the 2nd switch 37 can be set suitably in the range which does not interfere with the arrangement | positioning of the other transistor, capacitor, wiring, etc. which are contained in a pixel circuit.

The third switch 33 and the drive control element 30 can be designed to have almost the same structure as the first switch 32 and the second switch 37. For example, the first conductive thin film transistors may be used as the drive control element 30 and the first to third switches 32, 37, and 33, and they may be formed simultaneously. In this case, the pixel circuit can be formed in a relatively small process.

Next, the operation of the organic EL display 1 will be described in more detail.

4 is a timing chart illustrating an example of a method of driving the organic EL display of FIG. 1.

The scan signal line driver 12 sequentially outputs the scan signal Scan which makes the first switch 37 and the second switch 32 conduction to the scan signal line 36. The rise and fall of the scan signal Scan is gentle due to the wiring resistance and the capacitance. For example, as shown in FIG. 4, the potential waveform of the scan signal Scan is blunted by the time constant.

In addition, the scanning signal line driver 12 sequentially outputs the control signal G which makes the third switch 33 conduction to the row of the third switch 33. The light emission period is a period during which the third switch 33 is in a conductive state. In this case, video signals are written in units of rows, and a period in which one row is written is a light emission period in another row. Usually, in the signal writing period, the third switch 33 is in a non-conductive state, and the display element 30 and the pixel circuit are electrically insulated from each other.

In the writing period, the scan signal Scan which makes the first switch 37 and the second switch 32 conduction is supplied to the scan signal line 36. Accordingly, firstly, the first switch 37 having the shallower threshold Vth1 is in a conductive state, and then the second switch 32 having the deeper threshold Vth2 is in a conductive state. At this time, the input signal Iin is supplied from the video signal line driver 11 to the pixel circuit through the video signal line 35. That is, the drive current corresponding to the input signal Iin flows to the drive control element. Accordingly, the gate potential of the drive control element 30 is set to a value corresponding to the input signal Iin.

Thereafter, the scan signal Scan supplied from the scan signal line driver 12 to the scan signal line 36 is supplied from an ON signal for bringing the first switch 37 and the second switch 32 into a conductive state. Is changed to the OFF signal which makes the non-conducting state. In connection with this, first, the second switch 32 having a deeper threshold Vth2 is in a non-conductive state, and then the first switch 37 having a shallower threshold Vth1 is in a non-conductive state. Therefore, leakage of charge from the capacitor 38 is prevented, and the gate potential of the drive control element 30 is maintained at a value corresponding to the input signal Iin.

In the light emission period, the third switch 33 is brought into a conductive state by the control signal G supplied thereto. Since the gate potential of the drive control element 30 is maintained at a value corresponding to the input signal Iin, a current almost equal to the input signal Iin flows through the organic EL element 20. That is, the organic EL element 20 emits light with luminance according to the input signal Iin.

In this manner, in this embodiment, the channel length L2 of the second switch 32 is set longer than the channel length L1 of the first switch 37. In this way, the threshold value Vth2 of the second switch 32 is deeper than the threshold value Vth1 of the first switch 37. As a result, when the same OFF signal is supplied to the gates of the first switch 37 and the second switch 32, the second switch 32 is turned off before the first switch 37 is turned off. It can be made into a non-conductive state. Therefore, according to this aspect, the organic electroluminescent display 1 by which in-plane nonuniformity of gradation distortion and brightness was suppressed can be implement | achieved.

Moreover, in the form mentioned above, although each of the 1st switch 37 and the 2nd switch 32 has one channel between a source and a drain, these switches may have a different structure. For example, a multi-gate structure having a plurality of channels between the source and the drain may be employed for the first switch 37 and the second switch 32. In this case, the total channel length L2 of the second switch 32 (= L2 ′ + L2 ″ + ···) is the total channel length L1 of the first switch 37 (= L1 ′ + L1 ″). If it is longer than + ·), the same effect as described above can be obtained.

5 is a plan view schematically illustrating a modified example of the pixel structure of FIG. 3. The multi-gate structure can be employed on one or both of the first switch 37 and the second switch 32. However, from the viewpoint of suppressing the influence of the OFF current on the display operation, it is preferable to employ a multi-gate structure for the second switch 32 as shown in FIG. 5.

It is preferable that the difference of the threshold value of the 1st switch 37 and the 2nd switch 32 is about 0.2V-1V. In this case, the 2nd switch 32 can be made into the non-conduction state more reliably, before the 1st switch 37 turns into a non-conduction state.

In the above-described form, although the thresholds are different in the first switch 37 and the second switch 32 using the channel length, these thresholds may be different in other ways. For example, the threshold value may be different between the first switch 37 and the second switch 32 using the number of channels. That is, even if the total value of the channel lengths is the same, when the number of channels of the second switch 32 is larger than the number of channels of the first switch 37, the threshold of the second switch 32 is the threshold of the first switch 37. Deeper than

Alternatively, the dose of impurities may be different in the first switch 37 and the second switch 32. For example, when the p-channel thin film transistor is used as the first switch 37 and the second switch 32, the dose of the p-type dopant to the channel of the first switch 37 is the second switch ( If the dose of the p-type dopant in the channel 32 is greater than the dose of the p-type dopant, the threshold of the second switch 32 is deeper than the threshold of the first switch 37.

The 1st switch 37 and the 2nd switch 32 from which the dose amount of an impurity differs can be manufactured, for example by the following method. That is, in the normal process of forming the thin film transistor, the number of times of doping impurities in the channel region of the first switch 37 is made larger than the number of times of doping impurities in the channel region of the second switch 32. For example, first, impurities are doped in the channel regions of the first switch 37 and the second switch 32. Then, the photoresist is used to mask the channel region of the second switch 32. Subsequently, impurities are doped again in the channel region of the first switch 37. In this way, the dose of the dopant to the channel of the 1st switch 37 becomes larger than the dose of the p type dopant to the channel of the 2nd switch 32. FIG.

In the case where the thresholds are different in the first switch 37 and the second switch 32 by using the dose amount of impurities, the dose amount is between 1 × 10 ¹¹ cm ⁻² and 5 × 10 ¹¹ cm ⁻² between those switches. It is preferred that the degree is different. In this case, more reliably, the 2nd switch 32 can be made into a non-conduction state, before the 1st switch 37 turns into a non-conduction state.

The threshold of the first switch 37 and the threshold of the second switch 32 can be different in another way.

6 is a sectional views schematically showing an example of a structure that can be employed in the first switch. 7 is a schematic diagram schematically showing an example of a structure that can be employed in the second switch.

The first switch 37 shown in Fig. 6 is a top gate p-channel thin film transistor. This thin film transistor includes a semiconductor layer in which a source S and a drain D and a channel Ch interposed therebetween are formed. The gate TG is disposed above the channel Ch via the gate insulating film GI. The gate TG is covered with the interlayer insulating film II, and the source electrode SE and the drain electrode DE are formed on the interlayer insulating film II. These source electrodes SE and drain electrodes DE are connected to the source S and the drain D, respectively, through through holes formed in the gate insulating film GI and the interlayer insulating film II.

As for the 2nd switch 32 shown in FIG. 7, the 1st switch 37 shown in FIG. 6 except the back gate BG is arrange | positioned under the channel Ch via the insulating film BI. It has the same structure as The bias which deepens the threshold value of the 2nd switch 32 is applied to this back gate BG. For example, the voltage between the back gate BG and the source S of the second switch 32 is set to about + 0.2V to + 1.0V.

When the structures of FIGS. 6 and 7 are employed in the first switch 37 and the second switch 32, respectively, the threshold of the second switch 32 is deeper than the threshold of the first switch 37. FIG. Therefore, also in this case, the second switch 32 can be brought into a non-conductive state before the first switch 37.

6 and 7 illustrate a top gate thin film transistor, the bottom gate type thin film transistor may be used as the first switch 37 and the second switch 32. Also in this case, when the back gate structure is adopted for the second switch 32, the threshold of the second switch 32 is deeper than the threshold of the first switch 37. FIG. In addition, the back gate here is the gate arrange | positioned facing a control terminal via a gate insulating film and a semiconductor layer.

The techniques described in the first aspect can be combined with each other. That is, in order to make the thresholds different in the first switch 37 and the second switch 32, a method using a channel length, a method using a channel number, a method using a dose of impurities, and a method using a back gate structure Two or more of these may be combined.

In the 1st aspect, in order to make the 2nd switch 32 into a non-conduction state before the 1st switch 37, the threshold value of the 1st switch 37 and the 2nd switch 32 differed. This time difference of switching can be generated by other methods.

8 is a plan view schematically showing an organic EL display according to a second aspect of the present invention.

This organic EL display 1 has the structure similar to the organic EL display 1 of FIG. 1 except the following structure. That is, in the organic EL display 1 of FIG. 8, the first switch 37 and the second switch 32 have the same structure. In addition, in this display 1, the control terminal of the first switch 37 is connected to the scan signal line 36 through the delay element 39, and the control terminal of the second switch 32 is the scan signal line 36. Is directly connected to the The organic EL display 1 of FIG. 8 can be driven by the same method as described with reference to FIG. 4 in the first embodiment.

9 is a diagram illustrating an example of a signal input to a delay element and a signal waveform output from the delay element.

The delay element 39 serves to delay the switching of the first switch 37. For example, as shown in FIG. 9, the delay element 39 smoothly raises and lowers the scan signal Scan input thereto and outputs it to the control terminal of the first switch 37. On the other hand, the same scan signal Scan as input to the delay element 39 is supplied to the control terminal of the second switch 37. Therefore, when the threshold value of the 1st switch 37 and the threshold value of the 2nd switch 32 are substantially the same, when the OFF signal is supplied to the scanning signal line 36 from the scanning signal line driver 12, the 2nd switch 32 will be carried out. ) Becomes non-conductive prior to the first switch 37.

Thus, also in the organic electroluminescent display 1 of FIG. 8, the 2nd switch 32 can be made into the non-conduction state before the 1st switch 37. FIG. Therefore, according to this aspect, the organic electroluminescent display 1 by which the gradation distortion and the in-plane nonuniformity of brightness were suppressed can be implement | achieved.

Various elements can be used as the delay element 39.

FIG. 10 is an equivalent circuit diagram illustrating an example of a pixel circuit employable for the organic EL display of FIG. 8.

In this pixel circuit, the resistance element 39R is used as the delay element 39. In this case, as shown in FIG. 9, the signal supplied to the control terminal of the first switch 37 is delayed with respect to the signal supplied to the control terminal of the second switch 32.

As the resistance element 39R, for example, a polysilicon layer may be used. The polysilicon layer used as the resistance element 39R can be formed simultaneously with the polysilicon layers of the drive control element 30 and various switches.

As the polysilicon layer, for example, an n ⁺ type polysilicon layer, a p ⁺ type polysilicon layer, an i type polysilicon layer, or the like can be used for the resistance element 39R. Of these polysilicon layers, the i-type polysilicon layer has the largest resistivity. Therefore, when the i-type polysilicon layer is used, even when the size of the resistance element 39R is reduced, the switching of the first switch 37 can be sufficiently delayed with respect to the switching of the second switch 32. For example, the area of the resistive element 39R can be about 400 µm ² to 1000 µm ² .

FIG. 11 is an equivalent circuit diagram illustrating another example of the pixel circuit employable for the organic EL display of FIG. 8.

In this pixel circuit, as the delay element 39, a diode 39D connected to flow a forward current from the control terminal of the first switch 37 to the scan signal line 36 is used. In such a pixel circuit, when the scan signal Scan falls, a forward current flows through the diode 39D. Therefore, the ON signal is supplied to the control terminal of the first switch 37 without delay or slightly delayed from falling of the scan signal Scan. Further, when the scan signal Scan rises, reverse bias is applied to the diode 39D, so that a leak current flows in the diode 39D. Therefore, 0FF signal is supplied to the control terminal of the 1st switch 37 delayed from the rise of the scanning signal Scan. That is, also in the pixel circuit of FIG. 11, the OFF signal supplied to the control terminal of the first switch 37 is delayed with respect to the OFF signal supplied to the control terminal of the second switch 32.

As the diode 39D, for example, a diode-connected thin film transistor can be used. Here, as shown in FIG. 11, a p-channel thin film transistor having a gate connected to a drain while being connected between the control terminal of the first switch 37 and the scan signal line 36 as the diode 39D is used. have. The transistor 39D connected in this way functions as a diode. When a diode-connected thin film transistor is used as the diode 39D, the diode 39D can be formed simultaneously with the drive control element 30 and various switches.

FIG. 12 is an equivalent circuit diagram showing still another example of the pixel circuit employable for the organic EL display of FIG. 8. In this pixel circuit, the first diode 39D1 and the second diode 39D2 are used as the delay element 39. These diodes 39D1 and 39D2 are connected in parallel between the control terminal of the first switch 37 and the control terminal of the second switch 32. In addition, the forward direction of the first diode 39D1 and the forward direction of the second diode 39D2 are reverse.

In such a pixel circuit, when the scan signal Scan falls, forward current flows through the first diode 39D1. That is, as the scanning signal Scan falls, the ON signal is supplied to the control terminal of the first switch 37. In addition, when the scan signal Scan rises, forward current flows through the second diode 39D2. The forward resistance of the second diode 39D2 is set to be delayed from the rise of the scan signal Scan so that the OFF signal is supplied to the control terminal of the first switch 37. When the forward resistances of the diodes 39D1 and 39D2 are set in this manner, the OFF signal supplied to the control terminal of the first switch 37 is delayed with respect to the OFF signal supplied to the control terminal of the second switch 32.

In the pixel circuit of FIG. 12, the delay time of the ON signal to be supplied to the control terminal of the first switch 37 can be adjusted in accordance with the forward resistance of the first diode 39D1. In this pixel circuit, the delay time of the OFF signal to be supplied to the control terminal of the first switch 37 can be adjusted in accordance with the forward resistance of the second diode 39D2. In other words, the delay time of the OFF signal can be set independently of the delay time of the ON signal. Therefore, when the structure of FIG. 12 is employ | adopted as a pixel circuit, design at higher degrees of freedom is possible.

As the diodes 39D1 and 39D2, for example, a diode-connected thin film transistor can be used. Here, as shown in FIG. 12, a p-channel thin film transistor having a gate connected to a drain while being connected between the control terminal of the first switch 37 and the scan signal line 36 as the first diode 39D1 is used. I use it. As the second diode 39D2, a p-channel thin film transistor connected between the control terminal of the first switch 37 and the scan signal line 36 and whose gate is connected to the source is used. The transistors 39D1 and 39D2 connected in this way function as diodes whose forward direction is reverse. When diode-connected thin film transistors are used as the diodes 39D1 and 39D2, the diodes 39D1 and 39D2 can be formed simultaneously with the drive control element 30 and various switches.

The techniques described in the second aspect can be combined with each other. For example, the delay element 39 may be used in which a resistance element 39R and a diode 39D are connected in series. Alternatively, the resistor 39R and the diodes 39D1 and 39D2 connected in parallel thereto may be used as the delay element 39.

The technique of the first aspect and the second aspect described above can be combined with each other. That is, as described in the first aspect, the thresholds of the first switch 37 and the second switch 32 may be different, and the delay element 39 described in the second aspect may be formed in the pixel circuit.

Still other benefits and modifications are easy for those skilled in the art. Therefore, in the broader aspect, this invention should not be limited to the specific description and typical form described here. Accordingly, various modifications are possible without departing from the spirit or scope of the general concept of the invention as defined by the appended claims and their equivalents.

Claims (15)

A first terminal connected to the first power supply terminal, a control terminal to which a video signal is supplied from the video signal input terminal, and a second terminal for outputting a driving current having a magnitude corresponding to the voltage between the control terminal and the first terminal; A drive control element having a; An organic EL element connected between the second terminal and the second power supply terminal, A capacitor, wherein one electrode is connected to the control terminal, the capacitor capable of maintaining a voltage between the control terminal and the first terminal in a magnitude corresponding to the video signal; According to the scanning signal, the video signal input terminal and the second terminal are connected to each other in the signal writing period, and the video signal input terminal and the second terminal are not connected to each other in the light emitting period following the signal writing period. A first switch for switching to According to the scanning signal, the control terminal and the second terminal are connected to each other in the signal writing period, and the control terminal and the second terminal are disconnected before the first switch is disconnected. An active matrix organic EL display provided with a second switch for switching over to. A drive control element having a first terminal connected to a first power supply terminal, a control terminal, and a second terminal for outputting a drive current having a magnitude corresponding to a voltage between the control terminal and the first terminal; An organic EL element connected between the second terminal and the second power supply terminal, A capacitor connected between the positive potential terminal and the control terminal; A first switch connected between the video signal input terminal and the second terminal; A second switch connected between said control terminal and said second terminal, A control terminal for controlling switching of the first switch is connected to a control terminal for controlling switching of the second switch, and the threshold of the first switch is shallower than the threshold of the second switch. The method according to claim 1 or 2, And the first and second switches are thin film transistors of a first conductivity type. The method of claim 3, And the channel length of the second switch is longer than the channel length of the first switch. The method of claim 3, And the second switch has a multi-gate structure. The method of claim 3, And wherein the first switch has a higher concentration of first conductivity type impurities in the channel region compared to the second switch. The method of claim 3, And the drive control element is a thin film transistor of a first conductivity type. The method according to claim 1 or 2, The absolute value of the difference between the threshold of the first switch and the threshold of the second switch is 0.2V to 1V. A drive control element having a first terminal connected to a first power supply terminal, a control terminal, and a second terminal for outputting a drive current having a magnitude corresponding to a voltage between the control terminal and the first terminal; An organic EL element connected between the second terminal and the second power supply terminal, A capacitor connected between the positive potential terminal and the control terminal; A delay element having an input terminal connected to the control signal input terminal and an output terminal for outputting a control signal supplied from the control signal input terminal; A first switch connected between the video signal input terminal and the second terminal; A second switch connected between said control terminal and said second terminal, And a control terminal for controlling switching of the first switch is connected to the output terminal, and a control terminal for controlling switching of the second switch is connected to the control signal input terminal. The method of claim 9, And the delay element is a resistance element. The method of claim 10, And the resistive element is a polysilicon layer containing impurities. The method of claim 9, And the delay element is a diode connected between the control signal input terminal and the control terminal of the first switch. The method of claim 9, The delay element has first and second diodes connected in parallel between the control signal input terminal and the control terminal of the first switch, and the forward direction of the first diode and the forward direction of the second diode are reverse. display. An active matrix substrate on which an organic EL element is to be formed, A first terminal connected to a power supply terminal, a control terminal to which a video signal is supplied from a video signal input terminal, and a drive current of a magnitude corresponding to a voltage between the control terminal and the first terminal while being connected to the organic EL element A drive control element having a second terminal for outputting a; A capacitor connected to the control terminal, the one electrode being capable of maintaining a voltage between the control terminal and the first terminal in a magnitude corresponding to the video signal; According to the scanning signal, the video signal input terminal and the second terminal are connected to each other in the signal writing period, and the video signal input terminal and the second terminal are not connected to each other in the light emitting period following the signal writing period. A first switch for switching to According to the scanning signal, the control terminal and the second terminal are connected to each other in the signal writing period, and the control terminal and the second terminal are disconnected before the first switch is disconnected. An active matrix substrate provided with a second switch for switching. A pixel electrode, A first terminal connected to a power supply terminal, a control terminal to which a video signal is supplied from a video signal input terminal, and a driving current having a magnitude corresponding to a voltage between the control terminal and the first terminal while being connected to the pixel electrode. A drive control element having a second terminal to output; A capacitor connected to the control terminal, the one electrode being capable of maintaining a voltage between the control terminal and the first terminal in a magnitude corresponding to the video signal; According to the scanning signal, the video signal input terminal and the second terminal are connected to each other in the signal writing period, and the video signal input terminal and the second terminal are not connected to each other in the light emitting period following the signal writing period. A first switch for switching to According to the scanning signal, the control terminal and the second terminal are connected to each other in the signal writing period, and the control terminal and the second terminal are disconnected before the first switch is disconnected. An active matrix substrate provided with a second switch for switching.

Images